Mobile electronic devices, such as handheld position sensing devices are battery operated and need to be power efficient. Also, other mobile electronic devices such as cellular telephones, internet appliances, personal digital assistants (PDA) and other devices are being used for more than just providing voice and visual communication between parties or user. Today, such electronic devices are equipped with device position determinators, such as global positioning system (GPS) measurement circuitry, signal triangulation circuits or other satellite and non-satellite based position measurement circuitry that are capable of determining the position of the electronic device relative to a given point. The presence of position measurement circuitry on mobile electronic devices facilitates new features or new feature combinations. For example, mobile devices, such as cellular telephones can be used by parents to track the location of children or teenagers and other services may use the location of the device to provide content, map information, directions and other information.
The on-board device position determinator periodically obtains position information regarding the location of the device. Periodic position updating provides the mobile, battery powered device with necessary position data to enable a location function. Once established, the position information may require refreshing periodically. The position information update rate depends on the type of application performed by the device. Some applications require constant position information updates. For example, when a device is used for tracking, or “geo fencing”, the position information must be frequently updated and reported to the cellular network. Vehicle navigation requires real-time position information to function properly. Other applications, such as emergency 911 locating, operate on a “locate on demand” basis and do not require frequent updates of position information. In addition, where periodic position information updating is required, the frequency of these updates depends on factors such as anticipated travel speeds or required accuracy such that, for example, vehicle navigation applications may require substantially higher position information update rates than pedestrian tracking applications.
Periodic position information determination may represent a significant power drain for a mobile device battery due to excessive current drain. For example, an on-board GPS receiver may draw an average current of about 35 mA when fully activated. During continuous vehicle navigation, a position information refresh rate of about 1 fix/second will result in a continuous current drain of about 35 mA. People tracking applications operating at a position information refresh rate of about 1 fix/minute may result in an average current drain of about 1.2 mA. Current drains at these levels are sufficient to significantly reduce the operating time for the mobile device. Premature interruption of service due to complete battery discharge is a serious issue if the mobile device is used for security or safety purposes. In addition, the need to frequently recharge the mobile device discourages use of the device and can be a serious issue for applications where, for example, a child must remember to frequently recharge the device. Reducing power consumption in location enabled battery powered devices is useful for improving product usefulness.